Genetic analysis of human lung carcinomas indicate that tumor suppressor genes may be inactivated during carcinogenesis and tumor progression. Since tumor suppressor genes may be in multiple functional classes, a comprehensive strategy for identification and functional analysis is required. For example, allelic deletion and somatic hybrid analyses are being used to identify the chromosomal location of putative tumor suppressor genes. We have examined 54 non-small cell bronchogenic carcinomas with 13 polymorphic recombinant probes. Among squamous cell carcinomas (SCC) loss of heterozygosity was more frequent than among adenocarcinomas (Ad) or large cell carcinomas. Loss of heterozygosity for chromosome 17p was found in 89% of SCC when compared to 18% of Ad. Mutations in p53, a putative tumor suppressor gene on 17p, were frequently found in human lung cancers. Allelic sequence deletion analysis of chromosome 11 revealed two commonly deleted regions (llpl3 and llpl5.5). Somatic cell hybrids between normal human bronchial epithelial cells and HuT292-DM, a lung carcinoma cell line, had a finite life span in vitro and were nontumorigenic in athymic nude mice. Both of these studies suggest that tumor suppressor genes may play a dominant role in lung carcinogenesis and provide in vitro model systems for isolating these genes by subtraction library and insertional mutagenesis technologies.